Data collection system having stationary unit with electromagnetic induction circuitry for bidirectionally relaying data

ABSTRACT

A system for collection of data and entry of the data to a host computer has a portable, hand held, data collector for collecting data and a stationary data relay for receiving the data from the data collector and for transmitting the data to the host computer. The portable hand held data collector includes a case of a size and shape to be held by one hand during use, a keyboard for inputting the data, displaying for displaying the data, memory for storing the data and an interface for transmitting the data to external. The data relay includes a case shaped to set the portable data collector thereon, of first interface for receiving the data transmitted from the data collector and of said interface for comunicating bidirectionally to the host computer.

BACKGROUND OF THE INVENTION

(i) Field of the invention

This invention generally relates to a data collecting system and moreparticularly to a system according to which portable data collectors arecarried by the users to collect the data, and the data are transferredto a central processing unit so as to be processed and stored therein.

(ii) Description of the Prior Art

A conventional data collecting system consists of connecting portabledata collectors directly to a central processing unit via acommunication line, in order to transmit and receive the data.

In the conventional data collecting system, however, the portable datacollectors are provided with an interface circuit that connects to thehost computer. Further, the interfaces that connect to the centralprocessing unit require an interface circuit or a connector that meetsthe ratings such s EIA RS 232C or RS 422, making it difficult to reducethe size and weight or to make the device moisture-proof. Moreover, thedata collectors are used at all times being powered by a cell. Torestrain the consumption of current by the circuits, therefore, it isnot feasible to use clock signals of a high frequency, and thetransmission speed of the interfaces is 9600 bps at the greatest.Furthermore, the connector which is attached and detached repetitivelyloses its reliability. Moreover, since the data are transferred in aone-to-one manner between the portable data collector and the hostcomputer, one of the portable data collectors occupies the centralprocessing unit, and other portable data collectors must wait for theirturns. Therefore, the efficiency of data transfer is very poor.

Even if the host computer transfers the same data which requires a longtime for transferring to a plurality of portable data collectors, thecentral processing unit has to transfer the data to each portable datacollector sequentially, and so it causes a waste of time.

SUMMARY OF THE INVENTION

According to a preferred embodiment of this invention there is provideda system for collection of data and entry of the data to a host computerwherein the system comprises a portable, hand held, data collector, forcollecting data and a stationary data relay for receiving the data fromthe data collector and for transmitting the data to a host computer. Theportable hand held data collector includes a case of a size and shape tobe held by one hand during use, a keyboard for inputting the data,display means for displaying the data, memory means for storing the dataand interface means for transmitting the data externally to the datacollector, the data relay includes a case shaped to set the portabledata collector thereon, first interface means for receiving said datatransmitted from the data collector and second interface means forcommunicating bi-directionally to the host computer.

It is therefore an object of this invention to provide a system whichexhibits a high transmission speed relative to the host computer. It isanother object of this invention to provide a portable data collectorwhich is small in size, light in weight, and which is moisture-proof.

It is a further object of the invention to provide as system whichconsumes low electric power.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the whole structure of a data collectingsystem according to the present invention;

FIG. 2 is a perspective view of a portable data collector and a datarelay;

FIG. 3, 4 and 5 are sectional views of major portions of the data relayaccording to the present invention;

FIG. 6 is a block diagram of the data relay according to the presentinvention;

FIG. 7 is a circuitry diagram of part of a serial interface for the datacollector;

FIG. 8 is a diagram showing the appearance of the portable datacollector according to the present invention;

FIG. 9 is a sectional view of an input key of the portable datacollector;

FIG. 10 is a functional block diagram of the data collector;

FIG. 11 is a flow chart illustrating the process by a process selectmeans;

FIG. 12 is a flow chart illustrating the operation for changing the keyfunction;

FIG. 13 is a front view of a portable data collector showing arrangementof the keys of the data collector;

FIG. 14 is a diagram of key functions that are allotted to the datacollector;

FIG. 15 is a diagram which illustrates the contents of the key processcorrespondence memory;

FIG. 16 is a diagram which illustrates a partly modified key function;

FIG. 17 is a diagram showing the contents of the key processcorrespondence memory;

FIG. 18 is a block diagram of the portable data collector;

FIG. 19 is a circuitry block diagram of voltage detector of the datacollector;

FIG. 20 is a block diagram of a display unit of the data collector;

FIG. 21 is a block diagram of part of a common signal generatingcircuit; and

FIG. 22 is a timing chart of common signal and segment signal.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the accompanying drawings stationary data relays S1 toSn shown in FIG. 1 are placed between portable data collectors H1 to Hmand a Host Computer 1, the communication is not performed directlybetween the portable data collector H1 to Hm and the Host Computer 1 butis performed relative to the data relays so as to be stored therein, andthe data are sent to the other unit from the data relays S1 to Sn. Thecommunication between the portable data collector H and the data relaysare performed by an electromagnetic induction circuits M1 to Mnemploying a coil, in order to eliminate the connector and to simplifythe interface circuit. The portable data collectors H1 to Hm are coupledto data relays S1 to Sn via electromagnetic induction circuits M1 to Mn.When the portable data collectors H1 to Hm are being carried, the datarelays S1 to Sn are not coupled to the portable data collectors H1 toHm, but wait for receiving the data. Further, the data relays S1 to Snand the portable data collectors H1 to Hn can be freely combined, andtheir numbers can be freely selected. FIG. 2 shows a method of settingthe portable data collectors H1 to Hm' to the data relays S1 to Sn. Ifthe portable data collector H1 is inserted and coupled into the datarelay S1, the data input to the portable data collector H1 are at oncestored in the RAM of the data relay S1. The Host Computer successivelyasks the data relays S1 to Sn in regard to whether there are data via acommunication line 2. Only when there are data, the data are transmittedand received between the Host Computer 1 and the data relay S1, and thedata in the portable data collector H1 are sent to the Host Computer 1.During this moment, other data relays S2 to Sn must wait forcommunications with the Host Computer 1. The communication line 2 isformed by either wire or radiowave. The data relays S1 to Sn are poweredby AC power supply or large capacity DC power supply.

In the above-mentioned system, the data flow as described below. Thatis, when the data are to be transmitted from a portable data collectorto the Host Computer, both the data collector and the data relay have acoil so that the data are transferred from the data collector to thedata relay by the electromagnetic induction at such a low speed as 2400bps, and are temporarily stored in the RAM in the data relay and, then,the data are transferred from the data relay to the central processingunit via a communication line at a speed as high as 9600 bps or more. Inthis case, it is also possible to change the data format. When the dataare to be transferred from the Host Computer to the portable datacollector, the flow of data is reversed. The interface between theportable data collector and the data relay is formed by using a coil inthe casing without using a connector. Therefore, the device exhibitsexcellent moisture-proof property. Further, since there is no connectorto be attached or detached, the reliability is not deteriorated.Moreover, since the transmission speed is as low as 2400 bps, the clocksignal frequency can be maintained small to consume reduced amounts ofelectric current. It is further allowed to use a button-type lithiumcell or a like cell, contributing to reducing the size and weight.Further, the communication is effected between the Host Computer and thedata relay at such a high speed that a problem is solved in that acommunication line is occupied by a portable data collector which makesthe communication, and the transmission or reception of data from otherportable data collectors must be waited for.

STATIONARY DATA RELAY

The stationary data relay serves for relaying data bidirectionallybetween the Host Computer and portable data collector by setting thedata collector on a receiving surface 2 shown in FIG. 2. The receivingsurface 2 is inclined by about 30 to 60 degrees so that the display unit3 can be easily seen by an operator. An overhang 4 is provided at aportion of the data relay S to receive the portable data collector M inparallel with the receiving surface 2 which is provided with a recesshaving a curved surface 5 of a radius R with the edge P of the overhangas a center as shown FIG. 3. The curved surface 5 is made similar to alocus that is drawn when the data collector M is turned with the edge Pof the overhang as a center.

The data relay and the data collector have respectively a coil 7, 6 forcommunication in a responsive portion to each other when the datacollector is set on the data relay. Because the receiving surface isinclined, the coil 9 is brought into intimate contact with receivingsurface 2, so that it is placed in position relative to the coil 7.

According to this embodiment, the data collector can be attached anddetached favorably if the ratios are selected to be T:D:L:R≈5:6:5:8.Further, the bottom of the portable data collector M is rounded asdenoted by r, so that it can be handled desirably. FIG. 4 is a sectionview of an embodiment where the angle of inclination is 60 to 90degrees. If the angle of inclination is close to 90 degrees, theportable data collector M may fall down forwardly. Therefore, a straightportion 8 is provided under the curved surface 5, so that the portabledata collector M is prevented from falling down forward by means of theedge P of the overhang and the straight portion 8.

As shown in FIG. 4 and 5 the portable data collector M can be insertedin the receiving portion with an attitude of either I or II. When it isinserted with the attitude of I, a portion Q of the portable datacollector M slides on the curved surface 5 of the receiving portion, sothat the attitude of the data collector is changed from I to II. To takeout the portable data collector M, it may be tilted forward; i.e., theportable data collector turns with the edge P of the overhang P as acenter, and is taken out without any trouble. Further, the overhang 4prevents the portable data collector M from escaping.

A circuitry block diagram of the stationary data relay is shown in FIG.6. A CPU 9 controls a RAM 10 and an I/O interface 11 in accordance witha program stored in a ROM 12. The data are transferred to, and receivedfrom the Host Computer 1 by a serial interface 13 relative to thecentral processing unit. The data are further transferred to, andreceived from, the portable data collector by a serial interface 14relative to the portable data collector. A printer drive circuit 15executes handshaking with the printer and produces a print output. Acircuit for driving the LED and buzzer 16 controls the LED and buzzer. Aswitch receiving circuit 17 informs the CPU 12 of the fact that theswitch is depressed.

If it is detected by the switch receiving circuit 17 that the portabledata collector is mounted on the data relay, the data are transferredto, and received from, the portable data collector via the serialinterface 14 relative to the portable data collector, and the data thatare received are temporally stored in the RAM 10. Simultaneously withthe above-mentioned procedure or after the above-mentioned procedure hasbeen finished, the data are transferred to, and received from, the HostComputer Via the serial interface 13 relative to the Host Computer. Thecircuit 16 for driving the LED and buzzer indicates that the data arebeing transferred. Moreover, the printer drive circuit 15, messages fromthe portable data collector, from the central processing unit, or fromthe data relay, are output to the printer. When an error has occurredduring the above-mentioned procedure, the circuit 16 for driving the LEDand buzzer informs the users of the occurrence of the error. If the HostComputer transfers the same data to a plurality of portable datacollectors, the data relay stores perpetually the data sent from theHost Computer into RAM and then the data relay transfers the stored datato a plurality of portable data collectors. A circuitry diagram of theserial interface 6 relative to the portable data collector is shown inFIG. 7. A transmitting terminal 18 for inputting a signal thereto fromCPU, the signal represents the data to be transmitted to the portabledata collector and is connected to a transmitting unit 19 which consistsof resistors 20 and 21, a transmitting transistor 22 and diode 23. Theanode terminal of the diode 23 is connected, via a contact point 24, toa tuning unit 25 which consists of a transmitting/receiving antenna coil7 and a tuning capacitor 27 that are connected in parallel with eachother.

A receiving circuit 28 comprises a coupling capacitor 29, resistors 30and 31, a clipping diode 32, a receiving transistor 33, and a resistor34, and includes a high-pass filter which consists of the capacitor 29and the resistors 30, 31 and which is connected, via the contact point24, to the transmitting unit 19 and to the tuning unit 25. The receivingterminal 35 is connected to the collector of the receiving transistor33.

The signal input to the transmitting terminal 18 is sent to the baseterminal of the transmitting transistor 22 via a transistor drive unitwhich consists of the resistors 20 and 21, and causes the transmittingtransistor 22 to be switched. When the transmitting transistor 22 isrendered conductive, the contact point 24 assumes the ground level. Whenthe transmitting transistor 22 is rendered nonconductive, the contactpoint 24 assumes a high level to excite the transmitting/receivingantenna coil 7. Under this condition, the signal is transmitted to thebase of the receiving transistor 33 via coupling capacitor 29, resistor30, clipping diode 32 and resistor 31, to render the receivingtransistor 33 off or on. Consequently, a signal appears on the receivingterminal 35 having a phase opposite to that of the signal input to thetransmitting terminal 18. Here, if the terminal 24 is poorly connectedor if the transmitting/receiving antenna coil 7 is broken, the receivingtransistor 33 remains non-conductive irrespective of whether thetransmitting transistor 22 is rendered conductive or nonconductive, andthe signal being transmitted does not appear on the receiving terminal35.

On the another hand a excessive signal is inputted to the transmittingterminal 18 or if supply noise is generated, diode 23 prevent a currentfrom base to collector.

The serial interface 13 relative to the central processing unit mayemploy the same circuit as one of the serial interface 14 abovedescribed. Also the serial interface may employ a EIA standardizedinterface, for example RS 422 or RS 232C for high speed interface.

PORTABLE DATA COLLECTOR

The portable data collector M for collecting the data and fortransfering the data to the stationary data relay has the display unit 3located on the upper portion of the case 37 as shown in FIG. 2. Theportable data collector also has input keys 38. These input keys 38 arearranged on both inner sides of the case 37 able to open as shown inFIG. 8. When a user inputs data, the user opens the case 37 anddepresses the keys 38.

FIG. 9 is a section view of an input key, wherein a menu paper 39describing menus is placed on a membrane switch 40 and the surface ofthe menu paper is protected by a protecting sheet 41. The menu paper 39consists of a paper produced from a printer and describes menus that areprinted thereon. The protecting sheet 41 has lines to meet the keys ofthe membrane switches 40. Each key has four menus and any one of them isselected by depressing a select key (not shown) in advance.

FIG. 10 is a functional diagram of the portable data collector.

The portable data collector registers processes received from anexternal unit and addresses of processes corresponding to all of thekeys in the RAM.

The addresses are changed by an external unit, so that the functions ofgiven keys can be changed.

A key input means 42 is connected to a process select execution means43. A key process correspondence memory 44 and a process memory 45 arealso connected to the process select execution means 43. The processmemory 45 consists of an initial registration process memory 46 and anadditional registration process memory 47. The key processcorrespondence memory 44 and the additional registration process memory47 are connected to a received data registration changing means 48 whichreceives signals sent from an external key process registration means49.

If now a key is input from the key input means 42, the process selectexecution means 43 selects a process that corresponds to the key fromthe key process correspondence means 44. The content of the selectedprocess is registered in the initial registration process memory 46 orin the additional registration process memory 47 in the process memory45 and the process select execution means 43 looks in the process memory45 for a process that is selected from the key process correspondencememory 44 and executes the process. Under the initial condition, thereis no content in the additional registration process memory 47. Theadditional registration process memory 47 is used for the first timewhen a process is registered therein by the external key processregistration means 49 via the received data registration changing means48. In response to signals from the external key process registrationmeans 49, the received data registration changing means 48 registers theprocess into the additional registration process memory 47 and changesthe content of the key process correspondence memory 44. The key processcorrespondence memory 44 stores the correspondence of processes relativeto the keys. By registering a new process into the additionalregistration process memory 47 from the external key processregistration changing means 49 in order to change the process of the keyprocess correspondence memory 44 relative to the keys, it is allowed tochange the functions of any keys.

FIG. 11 is a flow chart showing the flow of operation of the processselect execution means 43, and FIG. 12 is a flow chart of the operationfor changing the key functions. The invention will now be explained inconjunction with these flow charts. In FIG. 11, a key Ki is depressed ata step (1). The process select execution means 43 selects from the keyprocess correspondence memory 44 the address of a process thatcorresponds to the key Ki at a step (2). The process select executionmeans 43 looks in the process memory 45 for a process represented by theaddress of the selected process at a step (3), and executes the processat a step (4). By changing the address of the process corresponded tothe key in the key process correspondence memory 44, therefore, the keyfunction can be changed. When a new function that has not beenregistered in the process memory 45 is to be possessed by the key, theprocess should be newly registered from the external key processregistration means 49 via the received data registration changing means48. In FIG. 12, a new process is registered in the additionalregistration process memory 47 from the external key process changingmeans 49 via the received data registration changing means 48 at a step(5). Next, at a step (6), a key portion to change the function of thekey process correspondence memory 44 is changed into the address of anewly registered process by the external key process changing means 49via the received data registration changing means 48.

How the key functions are changed will now be described by way of aconcrete example of FIGS. 13 to 17. FIG. 13 is a diagram of the portabledata collector having 20 keys K1 to K20. FIG. 14 is a diagram in whichfunctions F1 to F20 are allotted to the Keys K1 to K20. That is, FIG 14describes the functions of the keys in such a manner that a process F1is performed if the key K1 is depressed, and a process F2 is performedif the key K2 is depressed. FIG. 15 shows the contents of the keyprocess correspondence memory 44 that satisfy the key functions of FIG.14. The address of the process F1 enters into a portion where is storedthe address of a process that will be executed when the key K1 isdepressed. Similarly, the address of the process F2 enters into aportion that corresponds to the key K2. Further, the addresses ofprocesses F1 to F20 are entered to correspond to the keys K1 to K20. Theprocesses F1 to F20 are registered in the initial registration processmemory 46 in the process memory 45, but are not registered in theadditional registration process memory 47. In practice, any processesmay be referred to as the processes F1 to F20; e.g., the key that isregistered at first may be processed. If now the key K1 is depressed,this fact is informed from the key input means 42 to the process selectexecution means 43. The process select execution means 43 selects, fromthe key process correspondence memory 44, the address of a process whichcorresponds to the key K1. Here, since the contents of the key processcorrespondence memory 44 are as shown in FIG. 15, the process F1 isselected and is executed. The practical contents of the process F1 arestored in the initial registration process memory in the process memory45. By forming the key process correspondence memory 44 as shown in FIG.15, the key functions can be arranged as shown in FIG. 14. Next, withreference to FIG. 16, the processes F5 to F20 are effected in the samemanner as described above without changing the functions of the keys K5to K20, but changing the processes F1 to F4 of the existing functions ofthe keys K1 to K4 into the processes F21 to F24 that have not beenregistered in the process memory 45. The processes F21 to F24 are newlyregistered in the additional registration process memory 47 in theprocess memory 45 by the external key process registration means 49 viathe received data registration changing means 48. The contents of thekey process correspondence memory 44 are then changed as shown in FIG.17 by the external key process registration means 49 via the receiveddata registration changing means 48. Namely, the address of process F21is entered into a portion in which is entered the address of process ofkey K1, and similarly, F22 is entered into K2, F23 is entered into K3,and F24 is entered into K4. Therefore, if the key K1 is depressed, theprocess select execution means selects the process F21 that correspondsto the key K1 in the key process correspondence memory 44 of FIG. 17,and executes the process that is stored in the additional registrationprocess memory 47. The key functions are thus arranged as shown in FIG.16. As described above, new functions can be imparted to given keys byregistering processes from an external unit into the additionalregistration process memory 47 and by changing the contents in the keyprocess correspondence memory 44.

FIG. 18 is a circuitry block diagram of the portable data collecterwhich realizes the functions abovementioned. Two high-performancelithium batteries are connected in series to form a cell 50, and aconstant voltage of three volts is obtained through a power sourcecircuit 51. The consumption of electric current increases with theincrease in the power source voltage. As the power source voltagedecreases, on the other hand, the operation frequency of each ICdecreases and the system becomes defective. A voltage of three volts issuitable for this system. A cell voltage detecting circuit 52 works todetect the drop in the cell voltage, and is indispensable from thestandpoint of collecting the data. Details of the circuit will bedescribed later. A ROM 53 stores an initial program which is necessaryfor starting the system and a subroutine that is frequently used.Practical procedure for collecting data and items of input keys are allwritten onto a RAM 54 from the data relay by the electromagneticinduction through a transmitting/receiving coil 6 and an interface LSIthat controls the coil 6. The CPU 55 and the interface LSI 56 have anoscillating circuit, respectively, and generate clock signals necessaryfor the driving. The CPU 55 oscillates at about 1 MHz, starts tooscillate only when an interrupt signal is received from the interfaceLSI 56 in response to key input or transfer of data, and ceases tooscillate after a predetermined process has been finished. The interfaceLSI 56, on the other hand, oscillates at all times. A cheaplyconstructed tuning fork-type quartz oscillator which oscillates at 38.4KHz can be used. A tuning fork-type quartz oscillator for timekeepingdevice which oscillates at 32,768 Hz is cheaper since it is used inlarge amounts. However, a quartz oscillator which oscillates at 38.4 KHzis used when it is required to set the transfer speed relative to theexternal unit to be an integral multiple of a standard value of 1200bps. Thus, the oscillating circuit is divided into two, and the one onthe CPU 55 side is not operated except for a required moment, so thatthe consumption of current is greatly reduced in average. The interfaceLSI 56 further has a communications control function necessary for thedata communication, a function for controlling the input keys 38, afunction for generating an operation confirmation sound signal, and afunction for controlling a variety of CPU's 55 and the display unit 57.The volume of operation confirmation sound can be increased ordecreased. A circuit for coupling to the data relay may employ the samecircuit shown in FIG. 7.

A display unit 57 consists of a common signal generating circuit 57a, asegment signal generating circuit 57b, and a multi-character-dot-matrixliquid crystal display 57c. The liquid crystal display must be driven byac signals to prevent it from deteriorating, and its contrast isadjusted by changing the amplitude of the ac signals. The portable datacollector which has collected the data then transfers the data to anexternal unit. At this moment, signals are transferred from theinterface LSI 56 to the data relay device via the transmitting/receivingcoil 6. After the data have been transferred, the contrast is decreasedto decrease the consumption of electric current by themulti-character-dot-matrix liquid crystal display 57c.

FIG. 19 is a diagram which illustrates in detail the cell voltagedetecting circuit 52 of FIG. 18. When the CPU 55 is not in operation, anHLT signal assumes the "L" level, whereby a transistor 58 is renderednonconductive to interrupt the supply of power to a voltage detectingelement 59, to thereby decrease the consumption of electric current.When the power source voltage is greater than about 3.3 volts, thevoltage detecting element 59 directly produces the power source voltage.Since a new cell produces a voltage of as great as 6 volts, the voltagedetecting element cannot be directly connected to the CPU 55. Therefore,the level is changed through a transistor 60. When the cell voltage isnormal, furthermore, the transistor 60 is rendered nonconductive so thatno electric current is consumed. When the cell voltage drops to lowerthan 3.3 volts, the element is not destroyed since the difference issmall relative to the power source voltage of an inverter 61 of the nextstage. The output of the inverter 61 passes through a CMOS analog switch62, and is read as an IO output into the data of the CPU 55.

The display unit 57 will now be described in detail with reference toFIG. 20. The common signal generating circuit 57a contains a display RAMand a character ROM (which are not shown), and is connected to the CPU55 through an address bus, a data bus and other signal lines. As asignal is sent in the form of ASC II codes or the like from the CPU 55,the common signal generating circuit 57a converts it into a characterpattern data, latches it, sends the data to the segment signalgenerating circuit 57b, and generates a common signal which will be sentto the multi-character-dot-matrix liquid crystal display 57c. Inresponse to the character pattern data from the common signal generatingcircuit 57a, the segment signal generating circuit 57b generates segmentsignals that correspond to dots of the multi-character-dot-matrix liquidcrystal display 57c. The contrast is changed by changing the peak valuesof common signals and segment signals by using a booster circuit in thecommon signal generating circuit 57a.

FIG. 21 is a diagram illustrating a part of the common signal generatingcircuit 57a. A gate control circuit 63 operates depending upon thecontrast data sent over the address bus and the data bus. A dividingresistor 64 is driven on a constant current, and a potential at a givenconnection point is taken out by an analog switch 65 controlled by thegate control circuit 63 and by a voltage follower 66.

FIG. 22 shows common signals and segment signals. The common signalshave peak values of four levels and the segment signals have peak valuesof three levels. The display element does not turn on when thedifference between the signals is one level but turns on when thedifference between the signals is four levels.

The liquid crystal display element can generally be regarded as acapacitor which, when an ac voltage is applied thereto, permits acurrent to flow through them depending upon the amplitude and thefrequency. An ac voltage of a certain value is normally applied also tothose segments that are not turned on, so that a current flows throughthem even when the polarity of the signal is changed. The current thatis consumed while the CPU 55 is not in operation consists of a currentthat flows through the interface LSI 56 and the display unit 57, and acurrent that flows through the liquid crystal display elements. Themulti-character-dot-matrix liquid crystal display 57c is considered tobe composed of a great number of capacitors, and consumes a largecurrent to produce the display. Considered below is the case where thecontrast is decreased. As the output of the booster circuit decreases,peak values of the common signals and the segment signals decrease,whereby the amplitude of the ac voltage applied to the liquid crystaldisplay elements decreases and the current flowing through themdecreases. This is the condition where the contrast is decreased. Here,attention should be given to the fact that a dc voltage should not beapplied to the liquid crystal display elements to prevent them fromdeteriorating.

The CPU 55 operates for a very short period of time, and an averagecurrent is considerably smaller than that which flows into the CPU 55when it is not in operation. Therefore, to decrease the current that isconsumed when the CPU 55 is not in operation serves as a key to the cellsystem.

The cell life will be calculated below based upon practical examples.

(1) It is presumed that the data are input and are transferred requiringa time of one hour.

(2) The CPU consumes a current of 1.2 mA when it is in operation. In theportable data collector which consumes a small current, however, the CPUis usually not in operation.

(3) When the CPU is not in operation, the current being consumed is 40uA when the contrast is the greatest and is 20 uA when the contrast isthe smallest.

(4) If the CPU operates for 100 seconds a day, the average current thatis consumed is calculated as follows:

in the case of non-changing the contrast

    100 sec.×1.2 mA/86,400 sec.+40 uA=41.39 uA

in the case of changing the contrast ##EQU1## (5) When a cell having acapacity of 120 mAh is used, the serviceable life is calculated asfollows:

in the case of non-changing the contrast ##EQU2## in the case ofchanging the contrast

What is claimed is:
 1. A data collecting system for collection of dataand entry of said data to a host computer comprising: a portable handheld data collector for collecting data and for transmitting said dataexternally of the data collector, the data collector comprisinga case ofa size and shape to be held by one hand during use, a keyboard forinputting data and having numeral keys and function keys, display meansfor displaying said data, memory means for storing said data inputted bya user, and interface means for transmitting said data stored in saidmemory means to a stationary data relay; said stationary data relayhaving means for receiving said data from said data collector and fortransmitting said data to said host computer, the data relay includingacase having means for removably setting said portable data collectorthereon, first interface means for receiving said data transmitted fromsaid interface means in said data collector, and second interface meansfor communicating bi-directionally to the host computer; wherein saidinterface means in said data collector and said first interface means insaid data relay have respective circuit means for transmitting said databi-directionally using electromagnetic induction, andwherein each saidcircuit means comprises a tuning unit having a coil, and a capacitorconnected in parallel with said coil for generating an electromagneticfield when data are transmitted and for generating an electric signal byelectromagnetic induction when data are received, a transmitting unitfor inputting an electric signal to said tuning unit when data aretransmitted, and a receiving unit for outputting said electric signalgenerated in said tuning unit as serial data, said transmitting unit andsaid receiving unit being coupled together through a capacitor.
 2. Thedata collecting system claimed in claim 1 wherein said transmitting unitcomprises a transmitting transistor and a transistor drive unitconnected to the base terminal of said transmitting transistor, saidtransmitting transistor further comprising an emitter-grounded circuit,and the collector terminal of said transmitting transistor beingconnected to said coil of said tuning unit through a diode.
 3. The datacollecting system claimed in claim 1 wherein said receiving unitcomprises a high-pass filter comprised of said capacitor coupling saidtuning unit and said receiving unit and a resistor connected in series,a receiving transistor and a resistor constituting an emitter-groundedcircuit, and a clipping diode which protects said receiving transistor.